1. Field of the Invention
The invention relates to a method and a device for monitoring a pressure sensor which sets the pressure in a pressure accumulator, in particular in a high-pressure accumulator for a fuel supply system.
High-pressure accumulators are used in fuel supply systems, primarily in fuel injection systems for internal combustion engines which operate with very high injection pressures. Such injection systems, which, in diesel engines, are known as common-rail systems, have marked advantages, as compared with conventional injection systems, in terms of flexibility and costs. In these injection systems, a high-pressure pump conveys fuel out of a fuel tank into the pressure accumulator, via which the fuel is then made available at injection valves which are provided in the cylinder heads of the engine. The process of injection into the cylinders is triggered by supplying current to the injection valves. The injection volume depends on the pressure present at the injection valves and on the duration of the current supply.
The pressure in the pressure accumulator is regulated by a pressure actuator which is set by an electronic engine control unit. This engine control unit, via a sensor connected to the pressure accumulator, also detects the pressure level, so that the pressure actuator can be adjusted correctly. The pressure sensor therefore also performs an essential function in setting the pressure in the pressure accumulator. A malfunctioning of the pressure sensor and the resulting error in the pressure control of the pressure accumulator may result in an impaired injection behavior and therefore in an impaired combustion characteristic, and this, in turn, may entail an increased emission of pollutants.
Pressure sensors which are equipped with a function monitoring device and with additional measurement transducers are known. However, these additional measurement transducers result in a considerable increase in the cost of manufacturing the sensors. Furthermore, such function monitoring devices must also be adapted in their construction to the respective circumstances in the internal combustion engine, thus incurring additional costs. Published German patent application DE 195 13 158 A1 discloses a method for detecting a leak in a fuel supply system, in which the gradient of the fuel pressure is evaluated in the system after the fuel pump has been switched off. A fault detection is carried out if the pressure reduction in a part of the fuel supply system takes place more quickly than expected. Furthermore, German Patent DE 41 31 401 C1 discloses a method and a device for monitoring pressure sensors in a medical operating system. The range of fluctuation of the pressure signals for a specific operating pressure, which are delivered by the pressure sensors to be monitored, is compared with a desired range of fluctuations for detecting faults.